High resolution mapping system

ABSTRACT

A synthetic array mapping system is disclosed that is operable from a moving craft so as to provide a high resolution map of an area such as a sector of the earth&#39;&#39;s surface. A coherent side looking redar system is provided in the moving craft to obtain and store varying frequency doppler history components of objects in the area to be mapped. The stored history components are then mixed with a swept oscillator signal. Difference signals developed by this mixing are applied to a narrow-band filter to compare the frequency of the difference signal with a predetermined pass band and develop mapping signals representing objects in a fixed angular position relative to the flight path of the craft.

limited tates Patent n 1 Herman et al.

[54] HIGH RESOLUTION MAPPING SYSTEM [75] Inventors: Elvin E. Herman,Pacific Palisades;

Henry L. McCord, San Pedro, both of Calif.

[73] Assignee: Hughes Aircraft Company, Culver City,Calif.

22 Filed: Dec. 27, 1960 21 Appl. No.: 78,768

[52] [1.8. Cl. ..343/5 PC, 343/5 R [51] Int. Cl ..G0ls 9/42 [58] Fieldof Search ..343/5 R, 5, 5 PC Primary Examiner-Carl D. QuarforthAssistant Examiner..l. M. Potenza Att0rney-W. l-l. MacAllister, Jr. andErnest L. Brown [451 Apr. 3, 1973 [57] ABSTRACT A synthetic arraymapping system is disclosed that is operable from a moving craft so asto provide a high resolution map of an area such as a sector of theearths surface. A coherent side looking redar system is provided in themoving craft to obtain and store varying frequency doppler historycomponents of objects in the area to be mapped. The stored historycomponents are then mixed with a swept oscillator signal. Differencesignals developed by this mixing are applied to a narrow-band filter tocompare the frequency of the difference signal with a predetermined passband and develop mapping signals representing objects in a fixed angularposition relative to the flight path of the craft.

16 Claims, 9 Drawing Figures 1 are/4.121,. I

PATENTEDAPRS ms 3 5,915

SHEET 2 [1F 8 PATENHIDM-m I975 3 7 5,915

SHEET 5 OF 8 Irma 1% Pmammm m3 SHEET 8 [IF 8 HIGH RESOLUTION MAPPINGSYSTEM This invention relates to mapping systems and particularly to aradar synthetic array mapping system that provides a map with a veryhigh degree of resolution of objects.

For mapping large areas of the earth from an aircraft or from a highvantage point, normal optical photography is conventionally utilized.However, photographic pictures are generally only obtainable in thedaytime and during the presence of favorable atmospheric conditions.Also, photographic techniques conventionally provide focusing at only asingle range or distance. It is often advantageous to be able to obtaina map over a wide area and regardless of the presence of an unfavorableatmosphere. Radar mapping systems provide a means to obtain a highresolution map irrespective of weather or lighting conditions.

Radar mapping systems operating from amoving craft may utilize a narrowpulse side looking radar system and a processor that responds to thedoppler frequency shift for determining the presence and the location ofobjects to be mapped. One processing system utilizes a plurality ofdoppler filters arranged in parallel for simultaneously processing radarinformation recorded from ground objects at a plurality of ranges. Thesignals passed through the doppler filters are then sampled and furtherprocessed for recording information on the final map. However, in thisarrangement, the phases of the incoming doppler signals are notcorrected, hence the doppler filters are only responsive to a shortduration interval of the total doppler history and the result is whatcorresponds to an infinity focused, or as it is sometimes called, anunfocused map. Although in principle this parallel processingarrangement can be focused at the ranges of the mapping coverages, ithas the disadvantage of complexity and excessive weight because of thelarge number of parallel elements required for mapping a large area.Another arrangement for radar ground mapping utilizes a coherent lightsource and an optical system to process stored radar information.Although this system can be focused at all ranges of interest, it isslow in operation because of limitations in obtaining high intensityalong with coherency in the light source. Further, it requires a storagemedia which does not degrade the coherency of the light. Also, theoptical system of this arrangement has the disadvantages of beingrelatively complex and bulky and requiring a large number of criticaloptical adjustments.

A requirement for a radar mapping system is that elemerits within thearea being mapped be distinguished or resolved as finely as possible inboth dimensions so that small details as well as gross patterns arerecognizable on the final map, that is, the system must have a highdegree of both range and azimuth resolution. The resolution of objectsin the area being mapped is determined in range by the effective pulseduration of the radar and is determined in azimuth by the angular sectorover which the signal return is combined. Conventionally a very largeantenna is required in order to obtain a high degree of azimuthresolution. However, an

antenna mounted on an aircraft or other vehicle is' limited in size byaerodynamic and other physical considerations. A synthetic array systemthat processes information received from a relatively small antenna soas to develop a synthetic antenna equivalent to a very large antennawould provide a high degree of angular resolution and be operable fromhigh speed aircraft. A simplified and reliable mapping system that has ahigh degree of azimuthal resolution and that provides focusing at allranges of interest so as to define small details of the area beingmapped would be very advantageous 1 to'the art.

It is, therefore, an object of this invention to provide a radar mappingsystem that has a high degree of resolution in azimuth.

It is a further object of this invention to provide a system thatprocesses radar information in a serial manner and at a rapid rate so asto form a simplified but high speed map-forming system.

It is a still further object of this invention to provide a syntheticarray radar system operable from a moving vehicle that resolves objectsutilizing a relatively small antenna with comparable resolution as wouldbe afforded by a conventional radar utilizing a relatively largeantenna, thereby providing an accurate and detailed map of a selectedarea.

It is another object of this invention to provide a system forsequentially and rapidly processing doppler information into a highresolution strip map form with a minimum of equipment.

It is another object of this invention to provide a mapping system thatprovides focusing of a synthetic array so that all ranges of interestare well defined on the output display.

Briefly, this invention is a radar mapping system operable from a movingcraft to form a synthetic antenna array so as to provide a highresolution map of an area such as a sector of the earths surface. Acoherent side looking radar system is provided in the moving craft toobtain varying frequency doppler history components of objects in thearea to be mapped. The doppler history components from different rangeintervals of the area being mapped are then stored on a twodimensionalmedium. A reading device then sequentially samples a portion of therecorded doppler history along each range interval. The resultant outputsignals which vary in approximately a linear fashion in frequency duringthe sample are then mixed with a signal generated by a swept oscillatorhaving a predetermined frequency variation. Difference signals developedby the mixing of the informational signal and the signal generated bythe swept oscillator are then applied to a narrow-band filter. Thisfilter compares the frequency of the difference signals with apredetermined pass band to develop mapping signals representing objectsin a fixed angular position relative to the flight path of the craft.The mapping signals are applied to a display and/or recording devicethat is controlled by the aircraft velocity and by the reading sequenceof the reading device to form indications of the objects in theirrelative positions within the area being mapped.

The novel features of the invention, as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the accompanying description, taken in connection withthe accompanying drawings, in which like characters refer to like parts,and in which:

F168. 1 and 2 are schematic block and circuit diagrams of the mappingsystem in accordance with this invention;

FIG. 3 is a schematic diagram of the moving aircraft and the area beingmapped for explaining the development of the doppler target historysignals;

FIG. 4 is a diagram of waveforms for explaining the operation of theradar system of FIGS. 1 and 2 to record doppler information of an areabeing mapped;

FIG. 5 is a schematic diagram of a portion of the recording film forexplaining the recording and reading of doppler information over aselected range relative to the position of the craft for the system ofFIGS. 1 and 2;

FIG. 6 is a diagram of waveforms of time versus voltage for explainingthe reading and displaying operation of the system of FIGS. 1 and 2;

FIG. 7 is a schematic graph of frequency versus time for explaining theoperation of the system of FIGS. 1 and 2 to develop a focused syntheticantenna array;

FIG. 8 is a diagram of waveforms of time versus voltage for explainingthe comparison operation of the filter of FIG. 2; and

FIG. 9 is a schematic diagram of a final map having range and azimuthdimensions developed by the system of FIGS. 1 and 2 representing similardimensions of the area being mapped in FIG. 3.

Referring first to FIGS. 1 and 2, the arrangement of the elements of themapping system in accordance with this invention will be explained. Inorder to perform reliable recording of information received from atarget, a coherent transmitter and receiver III is provided which mayinclude an antenna 12 fixedly mounted on the side of a craft and coupledto a duplexer 14. Because of the operation of the system of thisinvention to provide a synthetic array, the antenna 12 may have arelatively small width. For transmission of RF (Radio Frequency) energyinto space, a radar synchronizer 18 applies synchronizing pulses of awaveform 19 through a lead 20 to a modulator 22 where the synchronizingpulses are shaped or squared. The modulator 22 then applies thesynchronized modulator pulses through a lead 24 to a pulsed amplifier 26which amplifies and gates RF signals which are applied thereto through alead 28 from a single sideband (SSB) modulator 32. The pulsed RF signalsgated and amplified by the pulsed amplifier 26, as shown by a waveform36, are then applied through a lead 38 through the duplexer 14 and tothe antenna 12 for being transmitted into space.

When an RF signal containing a plurality of modulated pulsesrepresenting doppler mapping information is intercepted by the antenna12 after being reflected from a plurality of objects to be mapped (FIG.3), the intercepted signal is applied from the duplexer 14 through alead 40 to a mixer 42 to be heterodyned to an IF (IntermediateFrequency) signal on a lead 44. For developing the local oscillatorsignal for the mixer 42, a stable crystal IF reference oscillator 48 isprovided to operate at the IF frequency. The signal developed by theoscillator 48 is applied through a lead 50 to a crystal multiplier 54which multiplies the IF reference signal to a signal at radio frequencyminus the selected intermediate frequency. The signal developed by themultiplier 54 is then applied through a lead 56 to the mixer 42 so thatit can heterodyne the intercepted signal to form the IF signal on thelead 44.

In order to provide phase coherency between the transmitted and receivedsignals, the IF reference signal developed by the crystal oscillator 48is applied through a lead 58 to the single sideband modulator 32.

The signal on the lead 56 is also applied through a lead 60 to thesingle sideband modulator 32. Thus, a coherent radio frequency signalwhich is offset by the IF reference signal is developed by the singlesideband modulator 32 and applied through the lead 28 to the pulsedamplifier 26 for transmission into space.

In reception the IF signal carrying the doppler mapping information,after having been heterodyned in the mixer 42, is then applied throughthe lead 44 to an IF amplifier 64 and in turn through a lead 66 to amixer 68 which develops a video signal including pulse modulationcomponents having amplitude variations representative of the dopplerfrequency of the signals received from each point object to be mapped,as will be explained subsequently. The reference signal for the mixer 68is applied thereto through a lead 72 from a single sideband modulator 74which is controlled by the IF reference signal from the stable crystaloscillator 48 through a lead 78. In order that the doppler frequencycomponents may be shifted to a desirable operating range away from zerofrequency, an offset oscillator is coupled to the single sidebandmodulator 74 through a lead 82. The resulting output of the singlesideband modulator 74 is slightly offset in frequency from that of theIF reference oscillator 48. The video signal of doppler modulationcomponents, after being heterodyned downward in frequency in mixer 68 bythe offset IF reference frequency, is applied from the mixer 68 througha lead 84 to a video amplifier 85 which passes as the bi-polarity videosignal, only the lower sideband components developed by the heterodyningoperation in mixer 68. It is to be noted that a conventional phasedetector may be utilized to develop the video signals in place of themixer 68 and the video amplifier 85.

The video signal passed through the video amplifier 85 is appliedthrough a lead 86 to a range gating circuit 87 which is controlled bygating pulses of a waveform 88 applied thereto from a gate generator 90through a lead 92. The range gate generator 90 is synchronized with theradar system in response to synchronizing signals of the waveform 19received from the radar synchronizer 18 through a lead 94. Theinformational video signal consisting of doppler modulated pulses,

I after being gated to select a desired range of mapping,

is applied from the range gating circuit 87 through a lead to theintensity grid of a record scanning tube 98 of a storage device 99. Thecathode of the record tube 98, which tube may be a conventional cathoderay tube, is biased by an adjustable source of potential such as abattery 100 so that the modulated pulses of the video signals cancontrol the intensity of the electron beam. The vertical deflectionplates 101 and 102 may be coupled to a sweep generator 106 throughrespective leads 108 and 110. The range gate generator 90 is coupledthrough a lead 112 to the sweep generator 106 so as to provide avertical sweep on the leads 108 and shown by respective waveforms 116and 118 during the gating interval of the waveform 88. The sweep signalsof the waveforms 116 and 118 are inverted so that during the gatinginterval an electron beam is deflected along a vertical path indicatedby a trace 120 on the screen of the tube 98, the vertical distance ofthe trace 120 representing the range interval of the area being mapped,as will be explained subsequently. In order to maintain the trace 120 ina desirable horizontal position, horizontal deflection plates 124i and126 are biased at a desired fixed potential by an adjustable source ofpotential such as a battery 120.

The electron beam developed by the record tube 98 causes a beam of lightto be emitted from the screen of the tube 98 through a focusing lens 132to a storage film 134 having a dimension from top to bottom of varyingrange R corresponding to the area being mapped. The storage film 134 issuitably arranged between reels 135 and 137 to move at a precise rate ina direction indicated by an arrow 138 which, as will be explainedsubsequently, represents the flight path of the aircraft and the azimuthof the area being mapped. A suitable servo-motor 140 is coupled througha shaft 142 to the reel 135 to provide movement of the film 134 at adesired speed proportional to the velocity of the aircraft v, which maybe derived from a conventional airspeed indicator (not shown). In orderto provide for constancy of the final mapping scale factor parallel tothe aircraft flight path, the speed of a high resolution mapping film d(FIG. 2) should be maintained at a fixed proportion relative to the rawdata film 134. In the method shown the servo-motor 140 has a suitablemechnical connection 148 coupled to a gear box 150 (FIG. 2) so that adesired velocity relation is maintained between the speed of a movementof the film 134 and the high resolution map 15 (11G. 2). As the storagefilm 134 moves in the direction of the arrow 138 recording dopplerfrequency information as sinusoidal variations of intensity indicated ata single range interval by dots 158 representing the peaks of thedoppler modulation for convenience of illustration, the film isdeveloped in a suitable fast developer tank 162 so that, for example,the dots 158 become the more opaque areas on the film 13 8 as indicatedby doppler history dots 166.

It is to be noted at this time that the magnitude of the sinusoidalvariations of intensity on the recording film 134, as illustrated by thedots 166, is representative of the amount of reflection of point objectsto be mapped. It is to be understood that the storage device 99including the record tube 98 and the storage film 134 is only oneexample of various types of storage devices that may be utilized.

Now that the radar and intermediate recording and storage portion of themapping system has been explained, the arrangement of the elements ofthe sequential processor will be explained. A read scanning tube 170 ofa reading device 171 is provided to sequentially scan the recording film134 in horizontal essentially constant range lines such as 172 throughthe entire range interval R or over a raster or frame 173 shown on thescreen of the tube 170 and as frame or raster 174 on the film 134, sothat the bipolarity video doppler signals, recorded as sinusoidalvariations of intensity, develop variations in light level to be sensedby a photomultiplier tube 175. It is to be noted at this time that theframes such as 174 are continuously repeated as the film 134 moves inthe direction of the arrow 130.

The scan pattern of the read scanning tube 170 is controlled from aprogrammer 178 as seen in FIG. 2 which includes an oscillator 180 forproviding a signal at a stable readout line repetition rate. The signaldeveloped by the oscillator 180 is applied through a lead 182 to ashaping circuit 184 for developing rectangular pulses on a lead 188having a width 2, and

separated by a time interval I between pulses as shown by a waveform186. The signal developed by the oscillator is also applied through alead 190 to a frequency divider 192 and in turn through a lead 194 to apulse shaper 1% to develop rectangular pulses on a lead 197 having awidth t, and separated by a time interval t, as shown by a waveform 198.The interval t between pulses of the waveform 186 and the interval t,between pulses of the waveform 198 have a fixed relation forrespectively developing the range sampling scan indicated by the line172 on the recording film 134 and for developing the vertical componentof the raster such as 174. The waveform 186 is applied from the lead 188through a lead 200 to one end of the resistor 202 (in FIG. 1) and thewaveform 198 is applied from the lead 197 through a lead 204 to one endof a resistor 206 (in FIG. 1), the other ends of the resistors 202 and206 being coupled in common through a coupling capacitor 207 to thecathode of the read scanning tube 170. The cathode of the tube 170 iscoupled to ground through a resistor 209. The results of the summingaction of the resistors 202 and 206 in conjunction with the resistor 209bias the tube 170 to cut off during the presence of pulses of thewaveforms 186 and 198 so as to eliminate the electron beam duringflyback operation thereof.

A bootstrap sweep generator 212 in FIG. 2 responds to the pulses of thewaveform 186 on the lead 188 to develop horizontal sweep signals inpush-pull form as shown by waveforms 216 and 218. The horizontal sweepsignal of the waveform 216 is applied through a lead 220 to a horizontaldeflection plate 222 of the tube 170 and the horizontal sweep signal ofthe waveform 218 is applied through a lead 22 3 to the other horizontaldeflection plate 226. Thus, the horizontal sweep signals of thewaveforms 216 and 218 being repetitive each time interval t,, t, controlthe read tube 170 to develop the horizontal essentially constant rangesweep indicated by the lines such as 172 (FIG. 1) for scanning therecording film 134.

To control the vertical sweep of the read scanning tube 170 and tosequentially scan the film 134 at different range elements during thetime of each raster such as 174, a bootstrap sweep generator 230responds to the pulses of the waveform 198 to develop a vertical sweepsignal of a waveform 232 on leads 234 and 240 and an inverted verticalsweep signal of a waveform 236 on leads 230 and 248. The vertical sweepsignal of the waveform 232 is applied through the lead 240 to a verticaldeflection plate 244 of the tube 170 and the vertical sweep signal ofthe waveform 236 is applied through a lead 2 88 to a vertical deflectionplate 251 for controlling the electron beam of the tube 170 to scansequentially over each range element such as indicated by the line 172and over a plurality of constant range lines to produce a raster such as174. The intensity grid of the read scanning tube 170 is biased from avariable DC source such as a battery 254.

It is to be noted that the horizontal sweep signals developed by theread scanning tube 170 can be reversed in direction and the direction ofthe vertical sweep of the read scan tube 170 can also be reversed.However, when reversing the direction of the vertical sweep, it is alsonecessary to reverse the direction of the sweep on the display tube(FIG. 2) and the compensation for focusing at all ranges, as will beexplained subsequently.

The video signal developed by the photomultiplier tube 175 consists offrequencies resulting from scanning the recorded doppler frequencies ata high rate. Because these recorded doppler components are read out in atime interval much shorter than their original recording interval, allfrequency components are scaled upward in frequency by a constantfactor. These signals are applied through a lead 258 to a suitable videoamplifier 260 (FIG. 2) and in turn through a lead 262 to a mixer 264.The linearly varying output frequency of the swept oscillator 269 isapplied through a lead 270 to the mixer 264. This linearly varyingfrequency from the swept oscillator serves as a reference signal forcomparison with the varying frequency of sampled doppler history of thevideo signal on the lead 262. The reference signal developed by theswept oscillator 269 varies in frequency over a programmed excursion. Itis this programmed varying reference frequency which, when heterodynedagainst the recorded doppler histories, provides for focusing in theazimuth coordinate. If the reference frequency were maintained constantinstead of being swept in frequency during each doppler history readoutand assuming a straight line flight path, then the system describedherein would be focused at infinite range.

The oscillator 268 which may be of a conventional Hartley type iscontrolled through a lead 272 from a conventional reactance tube 274which in turn is controlled by the output from a variable gain amplifier275 through a lead 276. The variable gain amplifier 275 may be a pentodecontrolled in gain at its suppressor grid by the vertical sweep signalof the waveform 236 through a lead 276 while the input at its controlgrid consists of the horizontal sweep signal of the waveform 216 appliedthrough a lead 277. The variable gain accomplished in amplifier 275 bythe vertical sweep waveform 236 maintains the electronic focusingoptimum at all ranges of interest by varying the slope of the frequencyexcursion of the swept oscillator as a function of the range of thereadout trace; The output of the variable gain amplifier 275 providesthe waveform which controls the linear frequency variation of theoscillator 268. The rate of change of frequency is varied in accordancewith the range of the objects being sampled so as to provide a syntheticarray focused at all ranges of interest. The linear frequency variationdeveloped by the oscillator 268 is the reference signal on the lead 270and varies at a frequency rate representative of the returns fromobjects in a selected angular region viewed from the flight path of thecraft (FIG. 3). The signal representing the difference in frequencybetween the reference signal developed by the swept oscillator 268 andthe doppler history read from the storage film 134 is applied from themixer 264 through a lead 278 to the grid of an amplifier tube 280. Thecathode of the tube 280 is grounded and the anode is coupled through alead 283 to a filter 288 which may include a parallel coupled capacitor284 and an inductor 286 coupled between the lead 283 and a suitablepositive potential B+ applied to a terminal 287. The filter 288 isselected with a relatively narrow pass band so that only differencesignals having a selected frequency of interest applied from the mixer264 are not shorted to the B+ terminal 287. It is to be noted that asingle stage filter 288 is shown for simplicity of illustration butadditional tuned stages may be cascaded to alter the filter bandpasscharacteristic. The filter 288 provides integration and a comparison ofthe frequency of the difference signals with the pass band thereof sothat information obtained from objects over a selected angular zone fromthe flight path of the craft (FIG. 3) is passed therethrough, as will beexplained subsequently.

The lead 283 is coupled to the collector of a transistor 290 of adumping circuit 292 so that prior to the start of the sweep of thewaveform 216 the energy in the filter 288 is discharged. The transistor290 which may be of the n-p-n type has its emitter coupled to theemitter of a transistor 294 also of the n-p-n type, which in turn hasits collector coupled to the terminal 287. The bases of the transistors290 and 294 are jointly coupled to one end of a winding 298 of atransformer 300, the other end of the winding 298 being coupled to theemitters of the transistors 290 and 294. A second winding 302 of thetransformer 300 has one end grounded and a second end coupled to thelead 188 for responding to the horizontal pulses of the waveform 186before each sweep of the waveform 216. The transformer 300 may have apolarity arrangement indicated by dots 306 and 308 so as to bias thetransistors 290 and 294 into conduction during the occurrence of thepulses of the waveform 186. In the absence of a pulse of the waveform186, both transistors 290 and 294 remain nonconductive therebypermitting signals on the lead 283 to integrate in the filter 288, if ofa proper frequency.

The filtered and integrated signal on the lead 283 is applied through acoupling capacitor 312 to a lead 314 and in turn to an envelope detector316 for developing a detected signal indicative of the amplitude of thesignals integrated in the filter 288. The detected signal is appliedfrom the envelope detector 316 through a lead 317, a suitable amplifier318 and a lead 319 to the intensity grid of a high resolution displaytube 320 for controlling the intensity of the electron beam developedthereby. The display tube 320 has vertical deflectionplates 322 and 324coupled respectively to leads234 and 238 for responding to the verticalsweep signal of the waveforms, 232 and 236 to form a range deflectionindicated by a line 326 on the screen of the tube 320. The horizontaldeflection plates 328 and 330 maintain the electron beam at a fixedhorizontal position by a battery 332. For blanking of the electron beamof the tube 320 during flyback time, the cathode is coupled through a DCisolating capacitor 331 to the lead 197 to respond to the verticaltiming pulses of the waveform 198. A variable DC source of potentialsuch as a battery 333 is coupled to the cathode of the tube 320 througha suitable isolating resistor.

In operation the signal applied to the intensity grid of the tube 320controls the electron beam intensity during the vertical trace. Thistrace is imaged by a lens (not shown) onto the film 154. Theinstantaneous range position R of the electron beam is determined by thevertical sweep voltages of the waveforms 232 and 236. The optical imageof the electron beam records element by element a high resolution map onfilm 154.

This recorded film may move in a direction indicated by an arrow 335 onrotating reels such as 334 and 336 with the reel 336 controlled througha shaft 338 from the gear box 150 which is connected through themechanical connection 148 to the servo-motor Mt). For developinginformation recorded on the map I54, such as an object 342, a fastdeveloping tank 334 may be provided.

The recording film 134, the record scanning tube 98 and the readscanning tube 170 are enclosed in a light free area indicated by a box346 so that undesired light does not contaminate the information to berecorded or read onto the film 134. It is to be noted that in order toisolate the light source of the read scanning tube 170, the box 346 maybe divided between the read scanning tube 170 and the record scanningtube 98. Also, the high resolution display tube 320 and recording film154 are enclosed in a light free area indicated by box 350 so thatundesired light does not affect the final picture on the map 154.

Referring now to FIG. 3, as well as to FIGS. 1 and 2, the general theoryand operation of obtaining doppler target history in accordance withthis invention will be explained. An aircraft 354 with the antenna 12fixedly mounted to the side thereof may be moving in a straight linefrom a position 356 along a flight path 358 relative to a point object360. It is to benoted that in general the operation of the mappingsystem in accordance with this invention will be explained relative to asingle point to be mapped but that the operation is similar for aplurality of objects, each having a plurality of points thereon such asthe target 362. When the craft 354 is in the position 356, the main lobe364 of the antenna 12 does not illuminate the object 360 so thatessentially no doppler information is reflected therefrom. As the craft354 moves to a position 366, the main antenna lobe now in position 368begins to illuminate the point object 360 with electromagnetic energy.Since there is a component of velocity toward the target 360, thereflected energy is slightly shifted upward in frequency. This upwardfrequency shift or doppler signal when translated down to low frequencyis indicated by a waveform 370 at a maximum frequency of f for theillustrated lobe position 368. As the aircraft moves decreases towardzero. The waveform 370 shows an envelope or the modulation on the pulsetrain if it were not offset away from zero frequency. As the craft 354moves to position 372, the antenna main lobe has shifted to position 374and is now centered at the point object 360 and the doppler frequency onthe pulsed RF return has decreased to zero. When the craft 35 moves to aposition 378, the edge of the antenna lobe at position 380 isintercepting the object 360 so that the reflected RF energy has downwarddoppler shift. This doppler shift is shown on waveform 370 as amodulation envelope of the pulse train again increasing in frequencyaway from zero. By the time the antenna has reached position 378 thereceived signals from point object 360 have their most negative dopplershift which when translated give the waveform envelope 370 correspondingto frequency F Mm, Also, as the craft 354 moves to a position 382, theantenna lobe position 336 has moved beyond illumination of the pointobject 360 so that essentially no pulses are received therefrom.

' forward, the velocity component toward the target The doppler signalof the waveform 370 represents the envelope or modulation of thebi-polar pulse train of the single point object 360 after beingtranslated to a low frequency, but similar signals are also receivedfrom all objects to be mapped between an arbitrary range R and R andwithin the illumination area of the lobe positions such as 374. Becausethe doppler envelope signal of the waveform 370 passes through a zerofrequency, the offset oscillator of FIG. 1 is provided to translate allthe received signals to a slightly higher frequency f, than was shown inwaveform 370, thereby developing a pulse train having a modulationenvelope of a waveform 388 on the lead 84 which contains the samedoppler target information as the waveform 370 but varies between afrequency f f MAX and a frequency f f,, Mm +fi,. Thus, the previouslydiscussed modulation component of the waveform 370 is only shown forpurposes of explanation. Frequencies f' and f' 2 at the waveform 388 areshown to indicate the portion of the received frequencies which will beprocessed to form the final map image corresponding to point object 360.This portion of the received frequencies will also dictate the selectionof the program frequencies of the swept oscillator 269 of FIG. 2. It isto be noted that the selection of the program frequency range for theswept oscillator 269 determines the squint angle of the high resolutionsynthetic array beam relative to the flight path of the arrow 358 duringthe processing which in the example of FIG. 3 is selected to process theinformation broadside to the flight path of the craft. A distance Lwhich is equal to a selected segment of the flight of the craft 354while illuminating a point target such as 360 is also the length of thesynthetic array developed by the system in accordance with thisinvention, as will be explained subsequently Referring now to thewaveforms of FIG. 4, as well as to FIGS. 1, 2 and 3, the operation ofthe radar and recording portion of the system will be further explained.The RF transmitted pulses of the waveform 36 having a selected pulserepetition frequency are transmitted from the antenna 12 in response tothe synchronizing pulses of the waveform 19. The synchronizing pulses ofthe waveform 19 have an interpulse period representative of a rangeinterval between zero range R to total radar range R Pulsed signals arereflected over the entire range interval between R, to R from aplurality of targets such as 360 and 362 of FIG. 3, are intercepted bythe antenna 12, and contain pulse modulation doppler information foreach point target as indicated by the envelope of the waveform 370 ofFIG. 3. The intercepted RF signals are then heterodyned in the mixer 42to an IF signal as shown by the pulses of IF energy from a single pointtarget of a waveform 390, amplified and then applied to the mixer 68.These pulsed IF signals of the waveform 390 are then mixed with a signalat a frequency f, IF from the single sideband modulator 7 controlled bythe oscillator 48 and the offset oscillator 30) to provide a frequencyoffset modulated pulse train for each point object or target, theenvelope of the modulation being shown by the waveform 388 of FIG. 3 forthe point object 360. In FIG. 4 a few of the pulses of varying amplitudeincluding the doppler modulation are indicated for the single point 360by a waveform 391. The pulses of the llll waveform 391 vary in amplitudeand polarity in response to the phase relation between the signals ofthe waveform 390 and the offset mixing signal on the lead 7 2. Thus, thebi-polarity video amplitude variation of the pulses on the lead 84results from heterodyning the doppler shifted target echo componentsagainst an offset IF reference supplied to mixer 68 through lead 72 sothat the modulation envelope is made up of a train of bi-polarity pulsesvarying in amplitude due to the doppler frequency and the offset inresponse to the relative phase of the signals on the leads 66 and 72.The video amplifier 85 has a band-width sufficient to provide thedesired range resolution. For any single echo, the polarity andamplitude of the video signal such as the waveform 391 is directlydependent upon its phase in mixer 68 relative to the offset IF referenceapplied through lead 72. It is to be noted that although the waveform388 of FIG. 3 shows only the return from a single target, the compositesignal applied through the video amplifier 85 to the lead 86 may includea large plurality of pulsed echo signals derived from a plurality oftargets at different range and azimuth positions between the entireradar range R, to R From amplifier 85 the video signal is then appliedto the range gating circuit 87 which is controlled by the gating pulseof the waveform 88 to pass only a portion of the total video signal,representing information received between the ranges R and R (FIG. 3),to the intensity grid of the record scanning tube 98. The sweepgenerator circuit 106 responds to the range gating pulses similar to thewaveform 88 to develop a linear sweep as shown by the waveform 116during the range interval R to R which sweep voltage and an invertedlinear sweep of the waveform 118 are respectively applied to thedeflection plates 101 and 102. Thus, over the range interval to bemapped, the pulse trains such as the waveform 391 developed from the IFsignal of the waveform 390 and varying in polarity and amplitude toinclude doppler information similar to that of the waveform 388 of FIG.3 controls the intensity of the electron beam of the record tube 98 asit scans along the range line 120. The electron beam is deflectedvertically in synchronism with the time of return of the informationfrom various ranges between ranges R and R of objects to be mapped suchas the target 360. During each of a plurality of vertical sweeps-such asindicated by a line 392 on the film 134, pulses such as of the waveform391 applied to the intensity grid of the tube 98, increase and decreasethe intensity of the electron beam to record the doppler frequency as avariation of intensity around a grey level. For purposes of illustrationin FIG. 1, these intensity variations are indicated at the peakamplitude of their doppler modulation by the dots 158 on the film 134.In order that both positive and negative pulses can be recorded, therecord tube 98 electron beam is adjusted so that zero signal inputresults in an intermediate level of beam current. The amplitude of thepulse of the waveform 391 resulting from the reflectivity of the pointobject 360 modulates both upward and downward the intensity of theelectron beam of the tube 98. During the occurrence of each rangeinterval as determined by the waveform 88, a separate verticaldeflection of the line 120 develops an adjacent vertical deflection pathon the storage film 134 similar to the line 392 because of the movementof the film 134. Thus, as the storage film 1343 continues to move in thedirection of the arrow 138, pulses having the cyclic amplitude andpolarity variations of the waveform 388 are recorded thereon indicativeof the doppler frequency. It is to be noted that the intensityvariations depicted by the dots 158 are illustrated for only one pointtarget at one range interval. However, in addition other targets atother.

range intervals and other targets at the same range interval may recordsimilar intensity variations during each vertical sweep indicated by theline 3922.

Referring now to FIG. 5 as well as to FIGS. 1 through 4, the recordingoperation will be explained in further detail, primarily considering thedoppler envelope component of the waveform 388 developed from the singlepoint target 360. It is to be again noted that the signal of thewaveform 388 is an envelope representing the pulse train resulting fromthe phase relation of the offset IF reference signal to the pulsedsignal derived from the point target 360. Along the vertical sweep line392 (FIG. 5) during the first trace, amplitude variations of videopulses on the lead of the waveform 391 (FIG. 4) are indicated by theenvelope of the waveform 388. Thus, at a range element R whichrepresents the range of the point target 360 of FIG. 3, there isrecorded on film 134 a sinusoidal variation in film densitycorresponding to the change of phase of the echo return relative to thecoherent reference.

For convenience of illustration, the sinusoidal variations on the film134 of FIG. 5 are shown as a series of dots such as dot 396 on verticaltrace 392. These dots depict in the illustration the pointscorresponding to the peaks of the doppler modulation. As discussedabove, the sinusoidal variations such as at the range element R25) areformed from a plurality of pulses having an amplitude varying at thedoppler frequencies as shown by the waveform 391. At the lower peak ofthe waveform 388 the intensity of the electron beam of the tube 98 isgreatly decreased so that minimum film exposure is produced such as atthe position of the range element R during a later sweep indicated by aline 398. Successive vertical sweeps of the line 392 and those followingare continuous, each occurring during a pulse interval of the waveform36. In practice since it is the doppler components that are to be readout of the film 134 and not the individual pulses, it is necessary toadvance film 134 at a rate sufficient only to resolve the highestdoppler component of interest. Because the film travel is uniform, thelower frequency end of the doppler signal history of the waveform 388causes the peak amplitudes of the sinusoidal variations in recorded filmdensity such as indicated at dot 404 to be spaced at greater distancesalong the range interval R The sinusoidal variations in opticaltransmissivity of the film 134 along range element R are the direct 7number 1 of FIG. 5. If the above-described range focus correction werenot applied, the resolution of the system would vary somewhat fortargets not at the exact range of focus because of the variation of theslope of the doppler signals as indicated graphically by lines 422, 423and 424. However, the resolution varies only a small amount if the rangeof interest R to R is a very small percentage of the distance fromantenna 12 to R The horizontal sweep voltage of the waveform 216 (FIG.6) is modulated in slope in the variable gain amplifier 275 by thevertical sweep voltage of the waveform 232. The resultingslope-modulated horizontal sweep waveform is applied to reactance tube274 which in turn controls the frequency sweep of the oscillator 268.The signal on the lead 270 during each horizontal sweep indicated by thelines 410 and 412 of FIG. has a slightly different frequency versus timeslope as controlled by the vertical sweep voltage of the waveform 232.Thus, during each horizontal sweep of the reading frame, such as framenumber 1 of FIG. 5, the reference signal on the lead 270 is applied tothe mixer 264 with a frequency varying at the same rate as the dopplerhistory of any target which lies within the angular correlation zone andwithin the range being sampled.

Now considering only the doppler history from a single point target ofrange element R as graphically shown by line 422 in FIG. 7, thedifference frequency developed on the lead 278 (FIG. 2) is constantduring the horizontal sweep on which it is read in each scanning frame,but since each successive complete scanning frame examines a later timesegment of doppler histories, the difference frequency varies betweensuccessivescanning frames. Thus, the reference signal of the sweptoscillator as depicted by line 414 at a time r is compared with aportion of the doppler history or the sampled information of the line422 representative of the information of a point target recorded in therange element R only once during each reading frame, such as indicatedby frame number 1 of FIG. 5. This comparison develops a differencesignal on the lead 278 with a frequency Af Also, at frame number 2 time,r t, where t, is the time interval to perform the total number ofhorizontal sweeps of a reading frame, the swept oscillator 269 comparesa signal indicated by a line 426 to a portion of the doppler history ofthe line 422 of the same point target 360 to develop a difference signalhaving a frequency Af Thus, each comparison of the swept referencesignal with the sampled signal history occurs during a later timeinterval of its doppler history or in other words further along the line422. Therefore, this comparison continues for different portions of thedoppler history of the single point target at range R that is lateralong line 422 until in response to a reference signal excursion, line427, at a time t mi}, where m is the reading frame number, a signalhaving a difference frequency Af is applied to the lead 278 from themixer 264. As opposed to other values of the difference signals, thedifference frequency Af falls within the pass band of the filter 288which has a narrow frequency response centered at this absolutefrequency so that only during one or perhaps two or three horizontalsweeps near the time r mt, is a translated doppler signal heterodyned toa frequency which will integrate, or build up, in amplitude to itsmaximum value in the tuned filter. The signal level in the filter isdetected by the envelope detector 316 and will provide maximum output atthe end of the integration interval t in response to the sampling of thedoppler history 422 at the time mt,.

Although the comparison of the doppler history of the line 422 for thesingle point target 360 occurs only once during each frame of the readscanning tube 170, a similar comparison of other recorded dopplerinformation occurs during each horizontal sweep as indicated by lines410 and 412 of FIG. 5. Also, during each horizontal sweep manycomparisons are simultaneously made because many doppler histories arerecorded in each range element such as R because of obtainingreflections from a plurality of points on objects being mapped.

To further consider information recorded at other range elements of thestorage film 134, such as the doppler history depicted by the line 423and derived from stored information in the range element R of FIG. 5 andthe doppler history depicted by the line 424 and derived from storedinformation in the range element R,,, a similar comparison is made inthe mixer 264 between the swept reference signal and the sampledinformation. To accomplish focusing at all ranges over a time intervalof a complete reading frame, as the range being sampled varies between Rand R the slope of the reference signal on the lead 270 varies betweenthat of a reference signal 428 and 429 to compare with the frequencyslope of that range. Similar to the discussion above, when the frequencyof the difference signal developed by the comparison of the referencesignal of the line 428 with the sampled information of the line 423 (atrange R equals the frequency Af the difference signal at an absolutefrequency Af passes through the filter 288 indicating that the sampledinformation was derived from a target at minimum range broadside to theposition of the craft. Also, when the frequency of the differencesignals developed by the comparison of the reference signal at eachsequential range up to R or R with the sampled information of dopplerhistories recorded at sequential range element up to R equals thefrequency A f the difference signal passes through the filter 288indicating that the sampled information was derived from a targetbroadside to the craft at a corresponding range. It is to be noted thatthe frequencies f and f are defined respectively as (pf 1 Af and (pf zAf where p is the overall scale factor and corresponds to the ratio ofthe doppler input rate onto the film to the readout rate. Thus, dopplerinformation recorded on the storage film 134 is sequentially sampled inincreasing range elements during each frame and compared with areference signal varying in a frequency versus time slope in a similarmanner to the doppler history. This variation of the slope provideselectronic focusing at all ranges to the synthetic antenna arraydeveloped by the system in accordance with this invention. Thedifference signal developed by the mixer 264 is then compared with thepass band of the filter 288 which is tuned to a selected frequency AfThe frequency Af is chosen to lie outside the frequency of excursion ofthe programmed swept oscillator and also outside the readout(illuminated) target offset doppler frequency explained subsequently,which determines the point-topoint intensity of each picture element onthe final map. It is to be noted that doppler signals from other pointtargets may be recorded along the range element R but thephotomultiplier tube 175 responds to develop a composite signal whichcontains the spectral components of each recorded doppler signal. Theamplitude of the signal of the waveform 388 is shown constant forconvenience of illustration but in practice it will vary in amplitudeproportional to the reflectivity of that object and in accordance withthe antenna 12 illumination pattern as the craft moves forward. Thus,both the reflectivity of an object being mapped and the positionrelative to the moving craft are recorded on the intermediate or storagefilm 134.

Now that the recording of the doppler history on the film 134 has beenexplained, the sequential processing operation will be further explainedby referring to the waveforms of FIG. 6 as well as to FIGS. 1, 2 and 5.The programmer 178 of FIG. 2 controls the read scanning tube 170 of FIG.1 so as to sequentially illuminate or sample a portion of the dopplerinformation recorded and photographically developed on the storage film134. During a reading frame number 1 indicated by a scanning area orraster 409 (FIG. 5), the horizontal sweep signal of the waveform 216(FIG. 6) continues from time to t to t, with each sweep continuing forthe horizontal correlation time i followed by a short time interval t,for retrace. For example, between times (t t,) and t information is readfrom a range element R by a horizontal sweep indicated by a line 410(FIG. 5) and between the times (t 1 t,) and t, the information recordedon the range element R is read by horizontal sweep indicated by a line412. This sequential sampling continues during the reading of frame orraster number 1 over the range elements R, to R, so as to sample orinterrogate the doppler histories of each of the range elements. Thesinusoidal variations in transmissivity of the recorded filmcorresponding to doppler histories as illustrated by dot 158 (FIG. 1) orby dot 396 (FIG. 5) are sensed by the photomultiplier tube 175 todevelop a signal similar to the waveform envelope 388 but translated upto amuch higher frequency due to the rapid readout rate. At thetermination of the raster indicated by the area 409 as controlled by thevertical sweep signal of the waveform 232, a second frame or rasterindicated by the area 416 is initiated to again sequentially read therange elements R to R, so that a later segment of the time history ofeach range element is sampled and sensed by the photomultiplier tube175. During the time of the retrace of the tube 170 at the end of eachhorizontal sweep of the waveform 216, the electron beam is blanked toprevent a signal from being sensed by the photomultiplier tube 175during this retrace interval. Horizontal blanking pulses of the waveform186 are applied through the lead 200 and resistor 202 to the cathode ofthe read scanning tube 170 to prevent a retrace being developed on thescreen during each horizontal sweep. Also, to eliminate the retrace ofthe vertical sweep between the frames such as the reading frames 1 and2, vertical blanking pulses of the waveform 198 are applied through thesumming resistor 206 to the cathode of the read scanning tube 170.

The sampled doppler information signal sensed by the photomultipliertube 175 during each horizontal sweep of waveform 216 has a frequencyvariation corresponding to each targets original doppler history as itappeared during recording on the lead 84. Because the doppler history isread out in a time interval t, which is much shorter than thecorresponding time interval during which it was recorded, the readoutdoppler frequency history is multiplied by a frequency scale factor.This output signal after being amplified in video amplifier 260 isapplied to the mixer 264 for being compared with a programmed referencesignal developed by the swept oscillator 269. After being mixed with theprogrammed swept reference signal, the read-out doppler signals areappropriately selected in a tuned filter to provide outputs from objectsor targets when their doppler histories pass through the point wherethey are heterodyned to fall within the pass band of the tuned filter288. This point corresponds to a very narrow angular zone, fixedrelative to the velocity vector of the craft 354 of FIG. 3, andrepresents the angular correlation zone.

Referring now to FIG. 7, as well as to FIGS. 1 and 2, for explaining theoperation of the swept oscillator 269, a line 422 graphically representsthe frequency variation or the doppler history versus time on the lead262 (FIG. 2) for the point target 360 resulting from sampling of therecorded waveform 388 of FIG. 3. A line 423 indicates the frequencyvariation of the doppler history signal on the lead 262 received from apoint target (not shown) at the minimum range R on the line 372 of FIG.3 and a line 424 indicates the frequency variation of the dopplerhistory received from a point target (not shown) at the maximum range Ron the line 372. As shown in FIG. 3, the shorter the range of a pointtarget, the shorter is the time of illumination of the point target bythe antenna main lobe such as 374 because of the angular coveragepattern 0 of the antenna 12, and the longer the range, the longer is thetime of illumination of the point target. Thus, for the minimum range Rthe useful doppler return from a target occurs during a shorter intervalof time than for the maximum range R However, at the shorter range thedoppler frequency varies at a greater rate than at a longer range. As aresult, this variation in total duration of recorded doppler history ofeach point'target at different ranges does not adversely affect thecomparison operation of this system. In order to record a point targetsuch as 360 on the final map 154 at the proper position along the flightpath, the swept oscillator 269 which develops the swept reference signalis programmed so that when read scanning tube is horizontally scanningdoppler histories at intermediate range, the swept oscillator variesover a selected frequency interval f to f,,. Thus, in general thefrequency varying sampled doppler history is compared with the referenceswept frequency signal to develop a difference signal which is thencompared with the passband of the filter 288. However, as discussedabove, the target histories of objects at each range between R and Rhave a different frequency versus time slope. Therefore, electronicfocusing at all ranges between R and R is provided by including thevariable gain amplifier 275 (FIG. 2) to vary the frequency versus timeslope of the reference signal applied to the mixer 264 on the lead 270as the range being sampled varies during each reading frame such asduring frame range. Within the principles of this invention it should benoted that the doppler information can be sequentially sampled indecreasing range sequence providing that a corresponding variation ofthe reference signal slope is programmed and that the doppler historycan be scanned in reverse direction.

In order that at the termination of each horizontal sweep indicated bythe lines 410 and 412 of FIG. 5, the filter 238 will be rapidlydischarged, the pulsed signals of the waveform 186 (FIG. 6) are appliedto the dumping circuit 292 to bias the transistors 290 and 294 intoconduction and short out the capacitor 284 and inductor 286. It is to beagain noted that the doppler history for the point target 360 and forthe targets at minimum and at maximum range indicated by the lines 422,423 and 424 are only for single point objects and that for a pluralityof points and objects the operation is similar as described.

To further explain the operation of the filter 288, the differencesignal on the lead 278 is shown by a waveform 430 of FIG. 8. The signalon the lead 283 is shown by a waveform 432 of FIG. 8. At time I mt, thecomparison of the reference signal 427 of FIG. 7 and the doppler historyof the line 422 develops a difference signal of an absolute frequency AfThus, energy is applied at the resonant frequency of the tuned circuitfilter 288 made up of capacitor 284 and inductor 286. This sinusoidalwaveform at the difference frequency Af is integrated developing thesignal of the waveform 432 on the leads 283 and 314 between the times rmt, and 2 mt,. The signal of the waveform 432 results from sampledinformation derived from a single point target which has passed througha broadside position relative to the flight path of the craft. Theintegrated signal of the waveform 432 is then applied to the envelopedetector 316 to develop a detected signal of a waveform 434 during theinterval t,,, which detected signal after amplification in the amplifier318 is applied to the intensity grid of the display tube 320 fordeveloping an electron beam. It is to be noted that the voltage on thelead 319 in combination with the cathode bias is normally at a level tomaintain the tube 320 at cutoff. Thus, during the interval after r mt,,the tube 320 has brightened and exposed a point on the map 154indicative of the presence of a target such as the point target 360.When at resonance the slope and therefore the maximum level of thedetected signal of the waveform 434 is proportional to the amplitude ofthe difference signal of the waveform 430 which in turn is proportionalto the reflectivity of the point object. The display recording tube 320has vertical deflection plates 322 and 324 controlled by the verticalsweep voltages of the waveform 236 and 232 so that the information isrecorded along a range dimension varying from R to R that is, R to R,arranged vertically on the map 154. The reflectivity of an object beingmapped and its angular position relative to the craft determines theslope and the final amplitude of the detected waveform 434, and this inturn determines the final intensity of the electron beam of tube 320 asdiscussed above. The doppler history signals such as the waveform 388(FIG. 3) have an amplitude determined by the reflectivity of the objectsbeing mapped which determines the intensity of recording on the storagefilm 134 as illustrated by the dots on the figure. The amplitude of thesampled signal applied to the mixer 264 is proportional to the amplitudeof the waveform 388. The amplitude of the output difference signal ofthe waveform 430 on the lead 278 is directly proportional to the inputsampled signal level. This output difference signal amplitude as well asits frequency in turn determines the slope of the detected signal of thewaveform 434 applied to the intensity grid of the tube 320. In order toeliminate retrace signals, the vertical pulsed signal of the waveform198 is applied to the cathode of the tube 320. The dot 436 whichrepresents an unexposed point on the film 154 is then passed through thedeveloping tank 344 to form a dark element on the final map 154.

Referring now to FIG. 9 as well as to FIGS. 1, 2 and 7, the final map154 will be further explained. The vertical sweep of the electron beamof the tube 320 is continuous on the map 154 as indicated by lines 438and 440, each line requiring a time interval t,,. Thus, as indicated onthe line 438 each small portion or element represents a time t,, duringwhich correlation of the frequency of the swept oscillator 269 and thefrequency of the sampled doppler history is performed at a differencerange interval. When a difference frequency Af energizes the filter 288,an object is recorded on the map 154. As the map 154 continuously movesin a direction indicated by the arrow 335, the horizontal positionrepresents the azimuth of the area being mapped and the verticalposition on the map 154 represents the range position between R and RThe point target 360 of FIG. 3 thus develops the point 436 on the map154 and the large target 362 develops the indication 342 on the map 154.As discussed above, the reflectivity of the targets 360 and 362determines the degree of exposure of the recorded indications 342 and436. It is to be noted that the target elements 342 and 436 on the map154 are only an example of the many representations that are developedfrom an area being mapped.

The mapping system in accordance with this invention thus develops afocused synthetic antenna array having a length L resulting fromutilization of target doppler histories over a portion of length ofcraft movement during which the radar returnsfromobjects are recorded astheir amplitudes and phases vary in response to the movement of thecraft 354 as shown in FIG. 3. The portion of the total recorded dopplerhistory equivalent to, the length L (FIG. 3), over which the dopplerhistory is selected, is sampled and compared with the reference signalto determine the relative position of the craft and the target when theinformation was being recorded. Because of the focused synthetic array,which is approximately equivalent to an antenna having a length L, ahigh degree of azimuth resolution objects being mapped is obtained.Since this system can also be operated at infinity focus as mentionedearlier and in order to compare all-range-focusing versus in- 1 finityfocus their relative azimuth resolutions will be considered.

If an infinity focused (or as sometimes called unfocused) syntheticarray is formed, then letting D be the resolution distance at the point360 of FIG. 3 in a direction parallel to the flight path 358, theresolution for the infinity or unfocused antenna may be expressedD=L+RML where R is the range in FIG. 3 from the craft 354 and the pointtarget 360 and )t is the wave length of the transmitted RF frequency. Itcan be seen that the resolution distance D is thus limited for theunfocused antenna.

As was explained, the system in accordance with this invention provideselectronic focusing in azimuth by linearly sweeping the frequency ofoscillator 268 during each range element readout. Focusing at all rangesis further provided (when required) by controlling the slope of thisoscillator frequency excursion as a function of range. Thus, throughall-range focusing a very small resolution distance may be obtained asshown by the following equation for a focused antenna:

when R 2 eL/A where l is the length of the transmitting antenna 12 (FIG.3).

Thus, by increasing the distance L over which each target dopplerhistory is processed, a large synthetic equivalent antenna length isachieved, hence a very high resolution map may be developed. It is to benoted that if the data from the real antenna 12 of the craft 354 weredisplayed directly without synthetic array processing then the azimuthresolution distance D is approximately equal to RA/l where l is thephysical length of antenna 12. Because of the greater degree ofcorrelation possible, .the longer the sample length of processed dopplerhistory the greater the resolution up to the point where the resolutiondistance D approaches the real antenna length. Thus, for maximumresolution of objects, the doppler history interval processed f' 1 to f2 (FIG. 3) in response to a point at intermediate range may be selectedequal to the frequency range f to f which represents the maximum dopplerexcursion over which the target is illuminated.

Now that the operation of the system in accordance with this inventionhas been explained, an example will be given to further explain the highazimuth resolution thereof. The following example is chosen to provide afeet null-to-null resolution distance D, that is, two objects at least10 feet apart near the point target 360 of FIG. 3 in a directionparallel to the flight path 358 are distinguishable. The range R betweenthe flight path 358 and the point target 360 is 10 nautical miles orapproximately 60,000 feet which is the intermediate range of R and R Thefrequency of the RF signal transmitted of the waveform 36 (FIGS. 1 and4) will be selected in the X-band region so that the wave length A isequal to 0.1 feet. The pulse repetition frequency (PRF) of the waveform36 of FIG. 4 is selected as 2KC because of considerations mentionedbelow. The maximum PRF is determined by unambiguous range considerationsand average power requirements. The minimum PRF is set so as to minimizespurious angular lobes or ambiguities, that is, the PRF must be setsufficiently high that target doppler components arising within the mainantenna illumination pattern are sampled at least twice per doppler sinewave. The length L of the synthetic array developed by the system isderived from:

L RAID 60,000 0.1 /10 600 feet The constant velocity of the aircraft vis selected as 300 feet/second. Thus, the time to gather informationt,,, that is, to fly an equivalent synthetic array or length L, is t,L/v 600/300 2.0 sec. per array length. Stated differently t representsthe interval of doppler history to be read out and processed at the 10mile range. In reading out the recorded doppler history interval orsampling, the time required per range element corresponding to an arraylength L of information, t the readout line duration, is selected as53p. seconds.

The system thus has a scale factor p t, /t= 2.0 /53 X 10-6 sec. 37,800.p may also be defined as the time required to gather an array length ofdoppler information divided by the time required to process (read out)the same information.

Now to calculate the instantaneous doppler frequency f at any point xdistance at range R off of broadside:

Where 3,, the angle between a line broadside of the craft and a linefrom the craft to a particular object which is x feet from broadside ata range R.

To determine the maximum doppler frequency of interest let X L/2 andhence sin [3, L/2R.

At an azimuthal position corresponding to the end of the syntheticarray, the maximum doppler processing frequencies occurs, i.e., theseextremes correspond to the extreme values of the predetermined dopplerhisto ry which must be processed to obtain the desired broadsideresolution, D, and are:

f MAX E zva/ L/2R so C.P.S.

To avoid negative frequencies and to allow a clear spectral region tofacilitate processing, the lowest negative doppler frequency obtainedduring the real antenna beam illumination must be offset so that it nolonger reaches zero frequency. Assuming a physical antenna 12 (inFIG. 1) of 5 feet pointed exactly broadside, the null-to-null angularbeamwidth of the real antenna is 2' )./1= 0.2/5 0.04 radians or 229. Themaximum doppler frequency which would exist at the real antenna nullswould bef MAX 2V,,/)\ sin l.l4 or E 120 C.P.S. Thus, f,, m of waveform370 translates to f of waveform 388 where f and f are offset from f Mmand f MAX respectively by 120 cycles. All the real time instantaneousdoppler frequencies incur the same shift, e.g., in FIG. 3,f' 1 =f 1 +f150 C.P.S. and f' 2 =f 2 +fl, C.P.S. where f C.P.S- UDMS 1 C.P.S- and fS z C.P.S.) in this case.

In read out, due to the sequential method of processing, the aboveinstantaneous real time, doppler frequencies are translated by the scalefactor p, and are now:

Pfpus 1 =p( 5.670 m.c.

Pfnus 2=p(90) 3.402 m.c.

The oscillator program is now determined to have a frequency range f tof from (5.670 Af MC to (3.402 A f,;) MC where Af is the absolute centerfrequency of the pass band of the filter 288 of FIG. 2. In

order to minimize spurious angular responses, those read out dopplercomponents lying beyond f' 1 and f 2 will be filtered out in the videoamplifier 260. if Af is chosen as 2.5MC, the program of the sweptoscillator 269 of FIG. 2 varies between fsl 8.17MC tof 5 .902MC.

The vertical deflection time t, required to develop each frame of FIG. 5during reading from the storage film 134 is determined from theconsideration of the sampling theory that to resolve a distance D, therecorded information must be sampled every D/2 equivalent feet on thefilm 134. Each frame such as shown by the area 409 of FIG. 5 must becompleted before the film 134 moves an equivalent distance of D/2 feet.

Thus, (t t,.) D/2v =0.0l67 seconds which includes the flyback time t, ofthe waveform 232 of FIG. 6.

The speed v, of the film 134 of FIG. 5 is dependent on a number offactors including vehicle speed and resolution and may be selected as0.33 inch/second. At this film transport rate the film will haveadvanced 0.0055 inches between frames such as indicated by the areas 409and 416 of FIG. 5. At this film advance rate the spacing betweensuccessive sine waves of the maximum recorded doppler component to beprocessed (f 1 150 C.P.S.) is equal to 0.0022 inches. It is to be notedthat although the resolution D with the specific parameters chosen inthe above example was selected as feet, the system in accordance withthis invention is capable of an even higher degree of azimuthresolution.

Thus, there has been described a mapping system for use from a movingcraft that provides a high degree of azimuth resolution to objects beingmapped. Because a high degree of range resolution is available fromother radar techniques, a highly detailed map is obtained of a selectedarea to be mapped. For a given physical antenna size, the systemimproves azimuth resolution over that obtainable with direct display ofrecording of the radar output by developing a synthetic antenna arrayhaving a length determined by the azimuth resolution required and byproviding a swept oscillator to compensate for the phase rotation of theradar returns as the path length varies so as to develop mappinginformation with electronic all-range-focusing. The processing issequential so as to minimize the complexity and weight of the system.Because a synthetic antenna is developed a relatively small physicalsize antenna may be employed and an aircraft may travel at a highvelocity without affecting the aerodynamic operation thereof. Thesystem, in accordance with this invention, allows reliable mapping of asurface area such as of the earth regardless of atmospheric conditions.

What is claimed is:

1. A mapping system comprising coherent radar means for developingdoppler signals representative of position of an object to be mapped,recording means coupled to said radar means for storing said dopplersignals, reading means coupled to said recording means to developinformation signals, mixing means coupled to said reading means,oscillator means coupled to said mixing means for developing a frequencyvarying signal, said mixing means developing a difference frequencysignal, filter means coupled to said mixing means to pass saiddifference frequency signal at a selected frequency, signal formingmeans coupled to said filter means for developing a signal in responseto said difference frequency signal being past through said filtermeans, and map forming means coupled to said signal forming means fordeveloping an indication of said object to be mapped.

2. A mapping system comprising signal forming means for developingdoppler signals having frequency and relative time characteristicsrepresentative of position respectively in a first and a seconddimension of an object to be mapped, recording means coupled to saidsignal forming means for storing said doppler signals, reading meanscoupled to said recording means to develop information signals from thestored doppler signals, mixing means coupled to said reading means,oscillator means coupled to said mixing means for applying a referencesignal having preselected frequency characteristics, said mixing meansdeveloping a difference frequency signal, filter means coupled to saidmixing means to pass said difference frequency signal at a selectedfrequency representative of said first dimension, and map forming meanscoupled to said signal forming means and to said reading means torespond in said second dimension for developing an indication of saidobject to be mapped.

3. A synthetic array system operable from a craft moving relative toobjects to be indicated over a range interval from the craft comprisingradar means mounted on the craft to illuminate the objects and developdoppler history signals therefrom as the craft moves, recording meanscoupled to said radar means for storing the doppler history signals inrange elements, reading means coupled to said recording means,programming means coupled to said reading means to control said readingmeans to sequentially sample the doppler history signals in each rangeelement, first comparison means coupled to said reading means and tosaid programming means for comparing the frequency of the sampleddoppler history with the frequency of a reference signal to develop adifference signal, second comparison means coupled to said firstcomparison means for comparing the frequency of said difference signalwith a fixed frequency, display means coupled to said second comparisonmeans, to said reading means and to said programming means for providingan indication of said objects.

4. A system operable from a craft moving past point objects fordeveloping indications of the objects over a selected range intervalfrom the craft comprising radar means mounted on said craft fordeveloping doppler signals of varying frequency in response to energyintercepted from each object while being illuminated by said radarmeans, storage means coupled to said radar means for recording thedoppler signals in range elements as the craft moves, reading meanscoupled to said storage means, programming means coupled to said readingmeans forsequentially sampling the doppler signals in each range elementto develop sampled signals indicative of the frequency variation of thedoppler signals, comparison means coupled to said reading means,reference means coupled to said programming means and to said comparisonmeans for applying a reference signal of varying frequency to becompared with said sampled signals to develop difference signals

1. A mapping system comprising coherent radar means for developingdoppler signals representative of position of an object to be mapped,recording means coupled to said radar means for storing said dopplersignals, reading means coupled to said recording means to developinformation signals, mixing means coupled to said reading means,oscillator means coupled to said mixing means for developing a frequencyvarying signal, said mixing means developing a difference frequencysignal, filter means coupled to said mixing means to pass saiddifference frequency signal at a selected frequency, signal formingmeans coupled to said filter means for developing a signal in responseto said difference frequency signal being past through said filtermeans, and map forming means coupled to said signal forming means fordeveloping an indication of said object to be mapped.
 2. A mappingsystem comprising signal forming means for developing doppler signalshaving frequency and relative time characteristiCs representative ofposition respectively in a first and a second dimension of an object tobe mapped, recording means coupled to said signal forming means forstoring said doppler signals, reading means coupled to said recordingmeans to develop information signals from the stored doppler signals,mixing means coupled to said reading means, oscillator means coupled tosaid mixing means for applying a reference signal having preselectedfrequency characteristics, said mixing means developing a differencefrequency signal, filter means coupled to said mixing means to pass saiddifference frequency signal at a selected frequency representative ofsaid first dimension, and map forming means coupled to said signalforming means and to said reading means to respond in said seconddimension for developing an indication of said object to be mapped.
 3. Asynthetic array system operable from a craft moving relative to objectsto be indicated over a range interval from the craft comprising radarmeans mounted on the craft to illuminate the objects and develop dopplerhistory signals therefrom as the craft moves, recording means coupled tosaid radar means for storing the doppler history signals in rangeelements, reading means coupled to said recording means, programmingmeans coupled to said reading means to control said reading means tosequentially sample the doppler history signals in each range element,first comparison means coupled to said reading means and to saidprogramming means for comparing the frequency of the sampled dopplerhistory with the frequency of a reference signal to develop a differencesignal, second comparison means coupled to said first comparison meansfor comparing the frequency of said difference signal with a fixedfrequency, display means coupled to said second comparison means, tosaid reading means and to said programming means for providing anindication of said objects.
 4. A system operable from a craft movingpast point objects for developing indications of the objects over aselected range interval from the craft comprising radar means mounted onsaid craft for developing doppler signals of varying frequency inresponse to energy intercepted from each object while being illuminatedby said radar means, storage means coupled to said radar means forrecording the doppler signals in range elements as the craft moves,reading means coupled to said storage means, programming means coupledto said reading means for sequentially sampling the doppler signals ineach range element to develop sampled signals indicative of thefrequency variation of the doppler signals, comparison means coupled tosaid reading means, reference means coupled to said programming meansand to said comparison means for applying a reference signal of varyingfrequency to be compared with said sampled signals to develop differencesignals at said comparison means, filter means coupled to saidcomparison means for comparing the frequency of said difference signalswith a predetermined frequency to develop a signal indicative of thepresence of objects at a fixed angle relative to the flight path of saidcraft, detecting means coupled to said filter means for developing adetected signal, and display means coupled to said programming means, tosaid reading means and to said detecting means for developing anindication of the point objects over said range intervals as said craftmoves along said flight path.
 5. A mapping system comprising radar meansfor developing doppler signals having frequency varying characteristicsand time of occurrence characteristics representative of position of anobject to be mapped, recording means coupled to said radar system forstoring said doppler signals, reading means coupled to said recordingmeans, programming means coupled to said reading means for controllingsaid reading means to read said doppler signals in a predetermined orderto develop informational signals, mixing means coupled to said readingmeans, swept oscillator means couPled between said programming means andsaid mixing means for developing a frequency varying reference signal,said mixing means developing a difference frequency signal, filter meanscoupled to said mixing means to pass said difference frequency signal atonly a selected frequency, detecting means coupled to said filter meansfor developing a signal in response to said difference frequency signalbeing passed through said filter means, and map forming means coupled tosaid detecting means to said reading means and to said programming meansfor developing an indication of said object to be mapped.
 6. A syntheticarray system operable from a craft moving relative to objects in a rangeinterval from the craft comprising a coherent transmitter and receivermounted on the craft to illuminate the object and receive dopplerhistory signals therefrom as the craft moves, recording means coupled tosaid receiver for storing the doppler history signals in range elements,reading means coupled to said recording means, programming means coupledto said reading means to control said reading means to sequentiallysample the doppler history signals in each range element, comparisonmeans coupled to said reading means and to said programming means forcomparing the frequency of the sampled doppler history with thefrequency of a reference signal to develop difference signals, filtermeans coupled to said comparison means for comparing the frequency ofsaid difference signals with a fixed frequency, detecting means coupledto said filter means for developing detected signals, and display meanscoupled to said detecting means and to said programming means forproviding an indication of said objects.
 7. A synthetic array systemoperable from a craft moving past point objects for developingindications of the objects over a range interval comprising radar meansmounted on said craft for intercepting doppler signals of varyingfrequency from each object while being illuminated by said radar means,frequency shifting means coupled to radar means for shifting saiddoppler signals, storage means coupled to said frequency shifting meansfor recording the shifted doppler signals in range elements as the craftmoves, reading means coupled to said storage means, programming meanscoupled to said reading means for controlling said reading means tosequentially sample the doppler signals in each range element and todevelop sampling signals representative of the frequency variation ofthe doppler signals, comparison means coupled to said reading means,reference means coupled to said programming means and to said comparisonmeans for controlling said comparison means to compare a referencesignal of varying frequency with said sampling signals to developdifference signals, filter means coupled to said comparison means forcomparing the frequency of said difference signals with a fixedfrequency to develop a signal indicative of the presence of objects at afixed angle relative to the flight path of said craft, and display meanscoupled to said programming means, to said reading means and to saidfiller means for developing an indication of the point objects over saidrange intervals as said craft moves along said flight path.
 8. A systemfor sequentially processing stored doppler information signals having afrequency variation indicative of the position of objects in a firstdimension and a time of occurrence indicative of the position of objectsin a second dimension, said doppler information being stored on astorage means in said first and second dimensions comprising readingmeans coupled to said storage means, programming means coupled to saidreading means for controlling said reading means to read a portion ofsaid stored frequency in said first dimension sequentially over apredetermined number of elements in said second dimension tosequentially develop a plurality of signals at frequenciesrepresentative of the stored frequencies of each of said elements,mixing means coupled to said reading means, oscillator means coupled tosaid mixing means and to said programming means for developing arepetitive reference signal of varying frequency in synchronism with thereading in said first dimension, said mixing means developing signalshaving a frequency equal to the frequency difference between saidsignals developed by said reading means and said reference signal,filter means coupled to said mixing means having a pass band centered topass the signals developed by said mixer at a predetermined differencefrequency, detecting means coupled to said filter means for developingan envelope signal from the signals passed through said filter means,and map forming means coupled to said programming means, to said readingmeans and to said detecting means to provide a representation of theobjects in said first and second dimensions.
 9. A system for continuallymapping an area in a selected range interval from a moving craftcomprising a source of doppler signals having time and frequencycharacteristics indicative of the position of objects in the area,recording means coupled to said source of doppler signals forsequentially recording the doppler frequency of said doppler signalsover the range interval, reading means coupled to said recording means,programming means coupled to said reading means for controlling saidreading means to form continuous reading frames each sequentiallyreading a portion of the doppler information of the doppler signals ateach of a plurality of predetermined range positions so as tosequentially form information signals from each doppler signalrepresentative of the frequency variation thereof, a mixer coupled tosaid reading means, a swept oscillator coupled to said mixer and to saidprogramming means for developing a comparison signal varying over apredetermined frequency range and in synchronism with the reading ofeach portion of the doppler information, said mixer developingcorrelation signals having frequencies equal to the difference of therecorded doppler signal and the comparison signal, a filter coupled tosaid mixer having a pass band centered at a predetermined frequency ofsaid correlation signals detecting means coupled to said filter meansfor developing a control signal, and recording means coupled to saiddetecting means, to said reading means and to said programming means forresponding to the time of reading said doppler information and tosignals passed through said filter means to provide an indication of theposition of the objects being mapped.
 10. A focused mapping systemoperable to map a range interval from a craft moving in azimuth relativeto objects being mapped including means for developing a plurality offrequency varying doppler signals having frequency and timecharacteristics representative of the position of the objects relativeto the position of the moving craft and for recording in parallel thedoppler signals over the range interval so that the information fromeach range forms a range element comprising reading means coupled to therecording means for scanning the recorded information, programming meanscoupled to said reading means for developing a first sweep signal havinga duration so said scanning means scans a portion of a range element andfor developing a second sweep signal so said scanning means sequentiallyand continually scans each range element for developing informationalsignals having frequencies proportional to the recorded doppler signals,mixing means coupled to said reading means, swept oscillator meanscoupled to said mixing means, variable gain means coupled to said sweptoscillator means and said programming means to respond to said first andsecond sweep signals to continually develop a reference signal having arate of change of frequency that varies during each of said first sweepsignals to conform to the rate of change of frequency of saidinformational signals to provide focusing, said mixer developing aplurality of correlation signals having a differEnce frequencyrepresentative of azimuth position of said objects, filter means coupledto said mixing means for passing said correlation signals at apredetermined difference frequency, and recording means coupled to saidfilter means to said programming means and to said reading means fordeveloping indications in range and azimuth of said objects in responseto signals passed through said filter means.
 11. A system operable tomap a range interval from a craft moving in azimuth relative to objectsbeing mapped comprising radar means for developing a plurality ofdoppler signals having frequency and time of occurrence characteristicsrepresentative of the position of the objects relative to the positionof the moving craft, recording means coupled to said receiver forsequentially recording in parallel said doppler signals over the rangeinterval so that the information from each range forms a range element,reading means coupled to said recording means for scanning the recordedinformation, programming means coupled to said reading means fordeveloping a first sweep signal having a duration so said scanning meansscans a portion of a range element and for developing a second sweepsignal so said scanning means sequentially and continually scans aportion of each of said range elements for developing informationalsignals having frequencies proportional to the recorded doppler signals,mixing means coupled to said reading means, swept oscillator meanscoupled to said mixing means, oscillator control means coupled betweensaid swept oscillator means and said programming means to respond tosaid first and second sweep signals to continually develop a referencesignal having a frequency variation over a selected frequency range,said mixer developing correlation signals having a difference frequencyrepresentative of a predetermined azimuth position of said objects,filter means coupled to said mixing means for passing said correlationsignals at a predetermined difference frequency, and recording meanscoupled to said filter means, to said programming means and to saidreading means for developing indications of said objects in azimuth andrange.
 12. A system for providing focused mapping of objects in a rangeinterval opposite a moving craft comprising pulsed coherent radar meanshaving an antenna mounted on the side of said craft for illuminatingsaid object being mapped and for obtaining doppler history signals ofsaid objects being illuminated, said doppler history signals varying infrequency and having a zero frequency when said object is opposite saidcraft, offset oscillator means coupled to said radar means for shiftingthe frequency of said doppler history signals so that said zerofrequency is at a selected frequency, an intermediate storage filmmoving with a predetermined velocity, a first scanning tube coupled tosaid offset oscillator means for applying an electron beam to the screenthereof for providing light spots thereon, control means coupled to saidfirst scanning tube and to said radar means for sweeping said electronbeam in synchronism with the range represented by said doppler historysignals, said first tube being biased to respond to the amplitudes ofsaid doppler history signals to said doppler history signals assinusoidal variations of intensity on said storage film in parallelrange elements, a second scanning tube mounted adjacent to said storagefilm to apply an electron beam to the screen thereof for providing lightspots which are imaged on said storage film, a programmer coupled tosaid second scanning tube for developing a first sweep signal so saidlight spots sweep a portion of the recorded doppler history of a rangeelement and for developing a second sweep signal so that said secondscanning tube sequentially sweeps through said portions of each of saidplurality of range elements in continuous scanning frames, photo sensingmeans mounted adjacent to said intermediate storage film for developingsignals during each frame having frequencies proportional to saidscanned portion of said doppler history signals, a mixer coupled to saidphoto sensing means, a swept oscillator coupled to said mixer, avariable gain amplifier coupled to said swept oscillator and to saidprogrammer to control said swept oscillator to develop repetitivereference signals of varying frequency during each interval of timeequal to said first sweep signal, said reference signals changing inrate of frequency variation as said second scanning tube scans differentrange elements, said mixer developing correlation signals havingfrequencies equal to the difference between the signals developed bysaid photo sensing means and said reference signals, filter meanscoupled to said mixer and having a selected frequency band to pass saidcorrelation signals at a predetermined frequency as integrated signals,directing means coupled to said filter means for developing an envelopesignal in response to said integrated signals, a third scanning tubecoupled to said detecting means and to said programmer to apply anelectron beam to the screen thereof and develop light spots thereon inresponse to said second voltage sweep, said light spots having anintensity controlled by said integrated signal, and a map film mountedadjacent to said third tube and coupled to said intermediate film tomove at a proportional velocity thereto, said map film responding to thelight spots of said third tube to provide focused indications of saidobjects being mapped.
 13. A system for mapping objects in a rangeinterval opposite a moving craft comprising pulsed coherent radar meanshaving an antenna mounted on the side of said craft for illuminatingsaid objects being mapped and for obtaining doppler history signals ofsaid objects being illuminated, said doppler history signals varying infrequency and having a zero frequency when said objects is opposite saidcraft, offset oscillator means coupled to said radar means for shiftingthe frequency of said doppler history signals so that said zerofrequency is shifted to a selected frequency, an intermediate storagefilm moving with a predetermined velocity, a first scanning tube coupledto said offset oscillator means for developing an electron beam toprovide light spots on the screen thereof, control means coupled to saidfirst scanning means and to said radar means for sweeping said electronbeam in synchronism with the range represented by said doppler historysignals, said first tube being biased to respond to the amplitudes ofsaid doppler history signals to record doppler history signals assinusoidal variations of intensity on said storage film in parallelrange elements, a second scanning tube mounted adjacent to said storagefilm to apply an electron beam thereto to provide light spots on thescreen thereof, a programmer coupled to said second scanning tube fordeveloping a first sweep signal so said light spots provided by saidelectron beam sweep a portion of the recorded doppler history of saidrange elements and for developing a second sweep signal so that saidsecond scanning tube sequentially sweeps through portions of each ofsaid plurality of range elements in continuous frames, photo sensingmeans mounted adjacent to said intermediate storage film for developingfrequency varying signals during each frame having frequenciesproportional to the frequencies of said scanned portion of said dopplerhistory signals, a mixer coupled to said photo sensing means, a sweptoscillator coupled to said mixer and to said programmer for developingreference signals during intervals of time equal to said first sweepsignals and varying in frequency over a range, said mixer developingcorrelation signals having frequencies equal to the frequency differencebetween the signals developed by said photo sensing means and saidreference signals, filter means coupled to said mixer and having aselected frequency band to pass said correlation signals at apredetermined frequency as integrated signals, detEcting means coupledto said filter means for developing an envelope signal in response tosaid integrated signals developed by said filter means, a third scanningtube coupled to said detecting means and to said programmer for sweepingan electron beam in response to said second sweep signal to developlight spots on the screen thereof, said beam and said light spots havingan intensity controlled by said envelope signal, and a map film mountedadjacent to said third tube and coupled to said intermediate film tomove at a velocity proportional thereto, said map film responding to thelight spots of said third tube to provide indications of said objectsbeing mapped.
 14. A synthetic antenna array system operable from a craftmoving relative to objects for indicating the objects with a high degreeof resolution comprising a coherent transmitter and receiver mounted onthe craft including an antenna to illuminate the object and receive aplurality of doppler history signals therefrom as the craft moves,storage means, recording means coupled to said receiver and to saidstorage means for storing the doppler history signals in range elements,reading means coupled to said recording means, programming means coupledto said reading means to control said reading means to sequentiallysample said range elements to form sampling signals, the amount ofinformation sampled in each range element being a predetermined portionof a doppler history signal, comparison means coupled to said readingmeans, swept oscillator means coupled to said programming means and tosaid comparison means for applying a reference signal thereto varyingover a preselected frequency range, said comparison means comparing thefrequency of said sampling signals with the frequency of said referencesignals to develop a difference signal, filter means coupled to saidcomparison means for comparing the frequency of said difference signalwith a fixed frequency pass band representing an angular position ofsaid objects relative to the craft, detecting means coupled to saidfilter means for developing a detected signal, and display means coupledto said detecting means to said storage means and to said programmingmeans for providing an indication of said objects, said systemdeveloping a resolution from said antenna substantially equivalent tothe resolution of a synthetic array antenna having a width equal to thedistance said craft moves to obtain said predetermined portion of adoppler history signal.
 15. A mapping system operable over an area in arange interval from a craft moving in azimuth relative to objects beingmapped comprising a coherent radar system including a transmitter andreceiver for developing a plurality of doppler signal components havinga frequency variation representative of the azimuth position of theobjects relative to the position of the moving craft and having apredetermined frequency when reflected from objects having apredetermined position in azimuth relative to said craft, a storagemedium movable at a velocity proportional to the velocity of said craft,recording means coupled to said receiver for sequentially recording assinusoidal variations of intensity said doppler signal components inparallel range elements, scanning means mounted adjacent to saidrecording means for scanning the recorded information, programming meanscoupled to said scanning means for developing a first sweep signalhaving a duration so said scanning means scans a portion of a rangeelement and for developing a second sweep signal so said scanning meanssequentially and continually scans each range element, sensing meansmounted adjacent to said recording means for developing informationalsignals having a frequency proportional to the recorded doppler signalcomponents, mixing means coupled to said sensing means, swept oscillatormeans coupled to said mixing means and to said programming means forcontinually developing a reference signal having a frequency variationover a selected frequency rAnge during a time interval determined bysaid first sweep signal, said mixer developing a plurality ofcorrelation signals having a difference frequency representative of apredetermined azimuth position of said objects, narrow band filter meanscoupled to said mixing means for responding to said correlation signalsat a predetermined difference frequency, dumping means coupled to saidfilter means and to said programming means for deenergizing said filtermeans at the termination of each of said first sweep signals, detectingmeans coupled to said filter means for developing a detecting signalindicative of said predetermined azimuth position of said objects, maprecording means coupled to said recording means for moving at apredetermined velocity indicative of azimuth position of the area, anddisplay scanning means coupled to said detecting means and to saidprogramming means for continually sweeping said map recording means witha time interval determined by said second sweep signal and responding tosaid detecting signal to provide an indication of the objects on saidmap.
 16. A system for providing focused mapping of objects in a fixedrange interval opposite a moving craft in response to doppler historysignals recorded on an intermediate storage film and having frequencyand time of occurrence characteristics representative of position of aplurality of objects, said doppler history signals being recorded asintensity variations in a plurality of range elements comprising a firstscanning tube mounted adjacent to said storage film to apply an electronbeam to the screen thereof for developing light spots which are imagedto said storage film, a programmer coupled to said first scanning tubefor developing a first sweep signal so said light spots resulting fromsaid electron beam sweep a portion of the recorded doppler history ateach of the plurality of range elements and for developing a secondsweep signal so that said first scanning tube sequentially sweepsthrough said plurality of range elements in repetitive frames, photosensing means mounted adjacent to said intermediate storage film fordeveloping informational signals during each frame having frequenciesproportional to said scanned portions of said doppler history signals, amixer coupled to said photo sensing means, a swept oscillator coupled tosaid mixer, oscillator control means coupled between said programmer andsaid swept oscillator for responding to said first and second sweepsignals to control said swept oscillator to develop reference signalsduring times equal to said first sweep signals and varying over apredetermined frequency range at a rate of frequency change indicativeto the rate of frequency change of said informational signals at eachrange interval, said mixer developing correlation signals having afrequency equal to the frequency difference between said informationalsignals and said reference signals, filter means coupled to said mixerand having a selected frequency band to pass said correlation signals ata fixed frequency, detecting means coupled to said filter means fordeveloping an envelope signal in response to signals passed through saidfilter means, a second scanning tube coupled to said detecting means andto said programmer for sweeping an electron beam across the screenthereof to develop light spots thereon in response to said second sweepsignal having an intensity controlled by said envelope signal, and a mapfilm mounted adjacent to said second tube and coupled to saidintermediate film to move at a proportional velocity thereto, said mapfilm responding to said light spots of said second tube to provideindications of said objects being mapped.